Opening of molybdenite ores and the electrowinning of rhenium

ABSTRACT

Disclosed is a method of separating molybdenum and rhenium contained in molybdenite bearing ores. The method involves contacting the ore with a solution of ammonium or a stable alkali metal or alkaline earth metal persulfate for a period of time sufficient to solubilize the molybdenum. The inability of the persulfate solution to solubilize the rhenium renders the process suitable for selective leaching of molybdenum with subsequent recovery of undissolved rhenium.

United States Patent [1 1 Carlin 1 OPENING OF MOLYBDENITE ORES AND THEELECTROWINNING OF RHENIUM Related US. Application Data {62] Division ofSer. No. 322,649, Jan. 11, 1973, Pat. No.

[52] US. Cl 204/105 R [51] Int. Cl C22d H00 [58] Field of Search 75/103,115, 121, 117,

[56] References Cited UNITED STATES PATENTS 669,440 3/1901 Frasch 204/112 A N O D E H3O (NH J 504 CATHODE 1 1 June 24, 1975 2,726,934 12/1955Forward et a1. 75/103 3,406,108 1011968 Radimer et a1. 204/82 FOREIGNPATENTS OR APPLICATIONS 1,051,51 1 2/1959 Germany 75/103 Primary E\'aminerR. L. Andrews Attorney, Agent, or FirmRoger S. Benjamin [57]ABSTRACT Disclosed is a method of separating molybdenum and rheniumcontained in molybdenite bearing ores. The method involves contactingthe ore with a solution of ammonium or a stable alkali metal or alkalineearth metal persulfate for a period of time sufficient to solubilize themolybdenum. The inability of the persulfate solution to solubilize therhenium renders the process suitable for selective leaching ofmolybdenum with subsequent recovery of undissolved rhenium.

1 Claim, 1 Drawing Figure CRYSTALLIZM (cu) ER PH ADJUST 4)a 4 ORE (Fe)(Cu) OPENING OF MOLYBDENITE ORES AND THE ELECTROWINNING OF RHENIUM Thisis a division of application Ser. No. 322,649, filed Jan. 11, 1973 nowUS. Pat. No. 3,8|6,588.

Molybdenum, found in the form of molybdenite, M03 is commonly separatedas the M082 concentrate obtained from porphyry copper ores. Theseconcentrates, which normally contain copper in the form of its sulfideand rhenium, may be relieved of their metal values by recovering thecopper using hydrometallurgical techniques and subsequent roasting ofthe molybdenite. Since M08 is recognized as an extremely stable species,this roasting requires extensive smelting facilities which, of course,are contributors to the pollution generally associated with the thermalprocessing of metal sulfides. In addition, the roasting process resultsin the conversion of rhenium values to volatile Re O-, which is lostfrom the roasting apparatus. The use of scrubbing devices will normallyrecover some but not all of the Re,O-, formed so that a portion of therhenium values originally held by the ore are lost. The use of rheniumin rhenium-platinum catalysts by the petroleum industry has resulted inits increase in price to a point where loss of even a small amount ofthe metal is to be avoided. A method for concentrating rhenium containedin molybdenite bearing ores so that it can be economically recovered byconventional methods would be desirable.

The present invention is a method for separating molybdenum and rheniumcontained in molybdenite bearing ores thereby concentrating the rhenium.The method involves contacting the ore with ammonium or a stable alkalimetal or alkaline earth metal persulfate for a time sufficient tosolubilize at least part of the molybdenum.

It has now been discovered that the molybdenum in molybdenite bearingores can be solubilized in persulfate solution. It has further beendiscovered that rhenium is essentially if not completely insoluble insuch solutions. The discovery that persulfate solutions possess suchselective solubility for molybdenum and rhenium provides a convenientmethod for their separation. The ore containing both metals is contactedwith a persulfate solution for a time sufficient to solubilize some orall of the molybdenum leaving the insoluble rhenium behind as a solid.The concentrated rhenium may be economically recovered. One method ofsuch recovery is to oxidize the rhenium in H 80 with permanganate orperchloric acid to form Re,O which can be distilled from the solution.An alternative method of recovery is to solubilize the rhenium with ahypochlorite and recover it by its electrodeposition.

It has further been discovered that copper is substantially more readilysoluble in persulfate solution than is molybdenum. Thus, when those orescontaining copper, molybdenum and rhenium are being treated, the presentinvention provides a convenient separatory technique. The ore iscontacted with the persulfate solution to solubilize copper untilmolybdenum is detected in the leach liquor. At this point, the leachliquor is removed from the leaching chamber and the ore is releached tosolubilize the molybdenum. When it is desired only to solubilize copperand molybdenum in order to effectuate their removal from the rheniumvalues and thereby concentrate the rhenium, the releaching step is notnecessary.

The persulfate ion is normaly provided by ammonium persulfate, however,it may be provided by any stable alkali metal or alkaline earth metalpersulfate having the requisite solubility. Barium and potassiumpersulfate are suitable. The persulfate leaching is normally carried outwith a persulfate solution having a concentration of from 10 to 500grams per liter of the persulfate, preferably ammonium persulfate, andat a temperature of from 20C. to ll0C., preferably from 25C. to 40C. Thepreferred temperature range is selected to optimize the balance betweenslow reaction rates at lower temperatures and persulfate decompositionat higher temperatures.

Since copper is more readily solubilized than molybdenum, the persulfateconcentrations and reaction temperatures will normally be lower whencopper is being solubilized than will be the case when the object is tosolubilize the molybdenum. For example, a solution having an ammoniumpersulfate concentration of 5 to 50 grams per liter and a temperature offrom 30 to 50C. may be used to solubilize copper and a solutioncontaining 50 to grams per liter ammonium persulfate and a temperatureof from 50 to C. used during the releach to solubilize molybdenum. Theseranges of ammonium persulfate concentration and leaching temperature arepreferred for most efficient separation of copper and molybdenum.

The ore or ore concentrate is normally ground to a particle size of l00325 mesh with a particle size of less than 200 mesh on the US. SieveSeries being typical. The persulfate solution is normally employed insufficient quantity to provide a slurry containing 5 to 60 percentsolids by weight with a slurry containing 10 to 20 percent solids beingpreferred.

Leach time will vary depending on such variables as particle size of theore, persulfate concentration and temperature. The degree ofsolubilization desired will also have an effect on the leach time.Substantially complete solubilization of copper can normally be achievedin a period of from 3 to 5 days in the preferred ranges of temperatureand persulfate concentration. A leach time of from 2 to 8 days willnormally be required to solubilize substantially all of the molybdenum.

The generation of (NH ),S,O for leaching of the ore may be carried outin an electrolytic cell as illustrated by the drawing. In operation, the(Ni-M 50 solution in the anode compartment of the cell ll is oxidized to(Ni-[3 8 0 In order to produce an economically attractive amount of thepersulfate, the ammonium sulfate concentration should be in the range offrom 100 to 800 grams per liter with a concentration of 300 to 500 gramsper liter being preferred and the potential between the electrodesshould be at least 3.5 volts with a potential of 4.5 to 6.0 volts beingpreferred. The (NI- 0 8,0 produced in the anode compartment along withsome unreacted (NH ),SO is removed through line 13 to compartment 15where the pH is adjusted to a level of 7 to 14 and preferably to a levelof from 9 to l l. A pH in the range of from 9 to 11 is preferred for anoptimum balance of leaching rate -vs.-- ammonium persulfatedecomposition rate. After adjustment of the pH, the ammonium persulfatesolution is fed via line 17 to the ore contained in leaching chamber 19.The ammonium persulfate solution is allowed to remain in contact withthe ore for a period sufficient to solubilize the desired amount ofmetal.

After the leaching of a typical ore concentrate, which comprises 90percent M05 5 percent CuFeS 3 percent H O, 0.2 percent Re and theremainder acid insolubles, the solution, which is essentially ammoniumsul- EXAMPLE l A sample of particulate (200 mesh) molybdenite oreconcentrate was used in the following experiment. The sample had areported assay of 1.1 percent copper, 1.9

fate containing solubilized metal species of copper, mo- 5 I lybdenumand iron, is removed from the leaching f if percent l? yl?denum (asmolybdenug chamber via line 2i leaving a rhenium concentrate bedlsulPercent r emum 5 percent water an hind. The rhenium concentrate is thenrecovered from 2 percent acid msolublfes' d the leaching chamber. Wheniron is among the solubi- A gram slampledo f0% f;fi, lized metalspecies, the pH is adjusted by addition of ID for each leachmg y an ff lw ml ammonia to the leach liquor in compartment 23 to a f ammomum pets gg 9 z by level of from 8 to 9 and the solution passed via line 25 r'l 3d grad? qf 2 a m i e to a crystalizer 27 where the solution isconcentrated t g l fi z 9 i z g and cooled to precipitate iron as (Nl-l),SO .FeSO i m g g r l t e l g The (Nl-L hSO solution containing solublecopper and to s e T l i Tr so u molybdenum is passed through line 29 tothe cathode Ir betel-mine fi t e g j' a l compartment of the cell 31. [nthe cathode comparta separate Tom I e y tratlon, using X-rayfluorescence procedures. The results presented ment, the solubilizedmetal species are reduced to their d h f h respective free metals andplated on the cathode. By b l heiermmmg t e i i o t g meta s in t e eaciquor, measuring t e vo urne an :ppheauon L commuzdbpotennal 5 specificgravity of the leach liquor, calculating the enum l? n s? ft h z t i ztaif z gg weight the metals solubilized and calculating the perw e'separa n 0 e e 0 cent of the metals solubilized on the basis of themetals I? leacfhmg chamzer :2 by i g z t d l in the concentrate. Todetermine if rhenium was being mg 0 pp W en m0 y enum 6 cc 3 solubilizedfrom the molybdenite ore, the leach liquor the leach q PP of a'conu'onedPotential is was concentrated fourfold and submitted for X-ray fluf'ysince p of f l-W and orescence analysis. The limit of detection ofrhenium lybdenum the leachmg operatlon norfPally by this procedure was25 parts per million. No rhenium be 100 P Cent effefllve. both p r ryhnique was detected in any solution indicating that less than 5 may beemployed to provide effective separation. percent was dissolved from theore.

After plating of the solubilized species of copper and 30 The results ofleaching molybdenite concentrates molybdenum, the solution in thecathode will consist with ammonium persulfate are set out in Table I.

TABLE I -t)t l ll Run Leach Temp. Concentration 91: Metal No. Time C.Grams/Liter solubilized Comments 1 1 hr. 50-70 200 l5.2 Cu N0 M0detected 2 24 hrs. 23-28 300 30.3 Cu N0 M0 detected 2 A 7 days 23-28 300[2.2 Cu Releach of solids from 9.7 Mo. Run 2 3 4 hrs. I00 200 28.9 Cu

l.7 Mo 4 9| hrs. 23-30 200 0.48 Mo Not analyzed for Cu 5 B days 50 I0084 Cu 0.66 Mo 5 A 24 hrs. 80 I00 4.25 M0 Releach of solids from Run 5not analyzed for Cu essentially of (NH ),S0 and water. This solution isre- While the present invention has been described with moved from thecathode compartment via line 33 and respect to certain details ofspecific embodiments, it is introduced to the anode compa t t 35 thsource f not intended that the invention be construed as limited ddi i l0 30 fo oxidation to (NHJISO? thereto except and insofar as details areset forth in the The anode and cathode compartments are separated by adiaphragm 35. This diaphragm is preferably a cation 1 clam: permeablediaphragm so that free metal cations or hymethod recovery of f mlybdemtedronium ions generated in the cathode compartment beanng i whlch ,methodcompnses the steps f and carried to the anode compartment through line33 f T 3 a {2 8 congemrzte 1: l gg can percolate through the diaphragmback to the cathi u f l y ciamactmg t e {no y elme ode com mg ore with asolution of ammonium or a stable alpaflmem' kali metal or alkaline earthpersulfate for a time The use of an electrolytic cell to both generateper- 0 suffieiem to convert at least part of the molybdesulfate andplate the solubilized metal improves the num, and other persulfatesoluble metals to their economics of the metal recovery operation. Othermetsoluble form, and als whose sulfides are solubilized by persulfatesolub. separating the insoluble rhenium concentrate from tions may berecovered in this manner. Examples of the persulfate solution, and suchmetals include silver, lead, zinc, nickel,cobalt and s u g the rheniumobtained from t p cadmium.

The invention is further illustrated by the following example.

and d. recovering rhenium from the solution of step (c) byelectrodeposition.

t I l 1' I!

1. A METHOD FOR RECOVERY OF RHENIUM IN MOLYBDENITE BEARING ORES, WHICHMETHOD COMPRISES THE STEPS OF: A. FORMING A RHENIUM CONCENTRATE AS ANESSENTIALLY INSOLUBLE SOLID BY CONTACTING THE MOLYBDENITE BEARING OREWITH A SOLUTION OF AMMONIUM OR A STABLE ALKALI METAL OR ALKALINE EARTHPERSULFATE FOR A TIME SUFFICIENT TO CONVERT AT LEAST PART OF THEMOLYBDENUM, AND OTHER PERSULFATE SOLUBLE METALS TO THEIR SOLUBLE FORM,AND B. SEPARATING THE INSOLUBLE RHENIUM CONCENTRATE FROM THE PERSULFATESOLUTION, AND